So, where is that mixed-signal behavioral model I ordered?

It has been said many time that SPICE, the analog engineers tool of
choice, is virtually the same as it was 20 years ago, while digital
engineers have been happily zooming up the evolutionary chain. There
have been a number of attempts to prod analog designers into closing
the gap with the introduction of behavioral modeling languages, and
more abstract system modeling solutions. However, they are not widely
adopted, much to the disappointment of the EDA vendors that provide
them. So why not?

Analog designs are, by their very nature,
multidimensional, and any assumptions you make to model one circuit are
completely inappropriate to model another. Modeling requires that you
make some decisions on which characteristics are important and which
are not, with more decisions needed on which conditions to model over,
and which to ignore. So standardized modeling techniques go out the
window, leaving every model as unique as the design it replicates.

This
isn't all doom and gloom, since there are many ways to leverage
behavioral modeling. In the early years of the behavioral languages,
users discovered that they could leave the design alone and instead
model the test fixtures. Since only the design under test remains in
SPICE, the simulations run faster and the test fixtures are more
readily reusable

Today, there are more tools coming out to
support the model creation process and they adopt a variety of
different strategies, from fully automatic to designer assisted. Also
the modeling languages themselves are getting faster and more
efficient, such that there is more impetus to push for modeling
expertise within a company.

My own personal opinion is that automated tools can be very
effective on some circuits, and useless on most, leaving many engineers
without support. So a company has to invest in some level of modeling
expertise to get the best out of the behavioral simulation technology.

Cadence
is taking a number of approaches in this arena. The first is to provide
a multi-disciplinary simulation solution to handle the broad range of
requirements. So with MMSIM 7.X from the Virtuoso platform, you can
happily simulate at the SPICE or fast-SPICE level and move up to the
behavioral level as it makes sense.

For model creation, Virtuoso Analog Design Environment GXL in IC 6.X
includes a Model calibration option. This enables experienced modelers
to create a library of adaptable models that are flexible enough to
adapt to a number of design variants. The end user can automatically
configure them to their specific designs, making reuse more practical
for the majority of engineers and across many design types. In both
cases the control is left in the hands of the design engineer.

This
is an interesting time, as the majority of designs now have both analog
and digital content. The need for an effective AMS solution with
modeling technology in support has never been more necessary and the
EDA vendors are rising to the challenge.